The technical field generally relates to monitoring fluid quality for aftertreatment systems, and more particularly but not exclusively relates to aftertreatment systems for internal combustion engines burning diesel fuel. Presently available internal combustion engines require aftertreatment systems in many cases to meet stringent emissions requirements. Some aftertreatment systems require specific fluids for operation. These fluids may require manual filling and due to their expense may be subject to bypass or manipulation, and/or subject to varying quality. One example of such a fluid is a mixture of water and urea called “diesel exhaust fluid”, which is utilized in selective catalytic reduction (SCR) aftertreatment systems. When the fluid is not present or has degraded quality, the system may need to adjust to meet emissions requirements, and further the fluid quality may need to be reported for maintenance or regulatory requirements. Direct measurements and verification of fluid quality are unavailable for most fluids. Therefore, further technological developments are desirable in this area.